System for the secondary suspension of a superstructure of a rail vehicle having an active spring element

ABSTRACT

System for the secondary suspension of a superstructure ( 1 ) in the case of a rail vehicle, having a hydropneumatic spring unit ( 3 ) as an active spring element which is placed between the superstructure ( 1 ) and a bogie ( 2 ) arranged below it and which ensures at least one raised traveling level (N F ) for the superstructure when the rail vehicle is traveling, by way of the hydropneumatic spring unit ( 3 ) as the active spring element, in the normal operation, in addition to the raised traveling level (N F ), a lowered station platform level (N B ) being adjustable for the superstructure ( 1 ), additionally at least one emergency spring cylinder ( 8 ) being provided which, when the system fails, ensures an emergency spring level (N N ) situated in-between for an emergency operation.

The present invention relates to a system for the secondary suspensionof a superstructure in the case of a rail vehicle, having ahydropneumatic spring unit as an active spring element which is placedbetween the superstructure and a bogie arranged below it and whichensures at least one raised traveling level N_(F) for the superstructurewhen the rail vehicle is traveling.

In addition to a secondary suspension used for the increase of comfortin the conveyance of passengers, a rail vehicle normally also has aprimary suspension. The primary suspension acts between the wheel axlesof the rail vehicle and the bogie and is used predominantly forabsorbing hard shocks to which the rail vehicle is subjected during itstravel as a result of an uneven rail guidance and the like. In contrast,a secondary suspension between a superstructure and railborne bogie of arail vehicle is used particularly for the additional vibration isolationof the superstructure in order to permit a particularly comfortabletravel by means of the rail vehicle when conveying passengers. In manycases, the secondary suspension also interacts with a roll control forthe superstructure.

From European Patent Document EP 0 690 802 B1, a secondary suspensionfor a rail vehicle is known which is constructed in the manner of ahydropneumatic suspension. The secondary suspension is achieved by meansof a hydraulic cylinder whose pressure chamber is connected with ahydropneumatic pressure accumulator. By way of the gas volume of thehydropneumatic pressure accumulator, a vertical spring effect isachieved. Furthermore, the hydraulic cylinder is equipped with apendulum support which forms a part of the piston rod which having ajoint at the upper end. During transverse movements, the pendulumsupport swings out, its end rolling on a corresponding surface. Sincethe radius of the end surface of the pendulum support is larger than thedistance of the joint from its supporting surface, a restoring momenttakes place during transverse movements which, as a result of theconstant distance of the joint from the supporting surface, isindependent of the spring excursion.

It is generally known to use conventional steel springs for thesecondary suspension in the simplest case, in addition to a pneumaticsuspension or hydropneumatic suspension. The superstructure is normallycushioned with respect to the bogie by way of two such passive springelements, in which case the bogie normally carries a pair of wheel axleswhich establish the contact with the rail.

However, when a secondary suspension is constructed by means of steelsprings as passive spring elements, the problem arises that thesuperstructure level may change as a function of the loading. In thesense of the present patent application, the superstructure level is thevertical level of the superstructure relative to the bogie or to theground.

From European Patent Document EP 0 663 877 B1, a system for thesecondary suspension is known which avoids this problem in that no steelsprings are used for the secondary suspension, but the secondarysuspension is implemented by way of a hydropneumatic spring unit. Thehydropneumatic spring unit consists of a spring leg and of ahydropneumatic pressure accumulator. These assemblies carry out thefunction of cushioning the superstructure as well as the function ofdamping the spring excursions. The spring leg is fastened on thesuperstructure and on the bogie. During a spring excursion, the pistonin the spring leg displaces a defined oil volume. In the hydropneumaticpressure accumulator connected with the spring leg, this oil volume actsagainst a gas cushion which is separated from the oil volume by amembrane and is therefore used as a springy element. The hydraulic fluidas the liquid column therefore takes over the function of the powertransmission. Vehicle vibrations during the travel are damped by meansof the nozzles housed in a nozzle block. As the load of thesuperstructure increases, the gas volume in the hydropneumaticaccumulators is compressed. Without any level control system, this wouldresult in a lowering of the superstructure, as in the case of theabove-described passive spring element. However, in order to avoid thislowering, the reduction of the gas volume has to be compensated byfeeding a corresponding amount of hydraulic fluid. For this purpose, thelevel control system is provided which carries out this compensation asa function of the distance between the superstructure and the bogiemeasured by means of a level sensor. The controlling of level changestakes place continuously and with little time delay while the vehicle isstopped. During the travel, the mean vehicle level is also continuouslymonitored and compensated.

In certain application cases, it is defined that, in addition to araised traveling level N_(F), the superstructure also has to take up astation platform level N_(B) level which is below it and which, in alowered position of the superstructure matches the door steps of therail vehicles with the height of the station platform, so that anentering and exiting becomes possible without steps. Furthermore, it hasto be provided that, despite such a lowered station platform levelN_(B), in the case of a system failure in the station, thesuperstructure of the rail vehicle, while being operated independentlyand manually, can also be brought to an emergency level N_(N) situatedabove, for resuming the travel. Furthermore, it is to be provided that,in the event of a system failure, the superstructure of the railvehicle, during the travel, is not lowered from the raised travelinglevel N_(F) to below the emergency level N_(N).

Despite the system failure, this emergency level N_(N) situated betweenthe lowered station platform level N_(B) and the raised traveling levelN_(F) permits an at least slow continued traveling of the rail vehicle.

In the case of the known system for the secondary suspension with anactive level control system, an emergency level N_(N), starting from atraveling level N_(F), however, can be adjusted only if sufficientstorage pressure is still present in the storage accumulator and theassigned valve is operated manually. Thus, an emergency level N_(N) doesnot have to be ensured under all circumstances.

It is therefore an object of the present invention to provide a systemfor the secondary suspension by means of which, despite a systemfailure, under all conditions, the superstructure, when stopped, cantake up an emergency level N_(N) from a lowered station platform levelN_(B) and, in the event of a system failure, during the travel, thesuperstructure is not lowered below the emergency level N_(N) from theraised traveling level N_(F).

Based on a system according to the preamble of claim 1, this object isachieved in conjunction with its characterizing features. The followingdependent claims reflect advantageous further developments of theinvention.

The invention includes the technical teaching that, by way of ahydropneumatic spring unit as an active spring element in the normaloperation, in addition to the raised traveling level N_(F), a loweredstation platform level N_(B) can be adjusted for the superstructure,additionally at least one emergency spring cylinder being providedwhich, when the system fails, ensures an emergency operation by means ofan emergency spring level N_(N) situated in-between. In this case, onthe one hand, the emergency spring level N_(N), in the event of a systemfailure, can be adjusted by an automatic moving-out of the emergencyspring cylinder. On the other hand, it is also conceivable as analternative, that the emergency spring level N_(N) occurs in the eventof a system failure by way of the already moved-out emergency springcylinder which therefore is already in readiness.

It is an advantage of the solution according to the invention that theadvantages of an active secondary suspension with respect to theflexible adjustment of different superstructure levels is connected witha passively functioning solution or an emergency operation which permitsat least a slow continued traveling of the rail vehicle. In principle,the emergency suspension is automatically activated when the systempressure decreases. During stoppage times, that is, in the area of thestation stop, this has the effect that the superstructure can reach ahigher emergency spring level N_(N) from the lower station platformlevel N_(B).

According to a preferred embodiment, the emergency spring cylinderconsists of a hydraulic tension cylinder whose piston can be moved outby means of a pressure spring. The force exercised by the pressurespring in the tensioned condition upon the piston is stored by arearward admission of pressure medium to the piston. When this rearwardpressure decreases, the piston of the tension cylinder carries out themove-out motion as a result of the now predominant spring force.

A particularly space-saving arrangement is achieved in that the pressurespring is produced of steel in the manner of a coil spring whichcoaxially surrounds the tension cylinder. As a result of thisarrangement of the pressure spring, which is exposed to the outside, theapplicable spring force can be maximized because of the large diameter.Simultaneously, the components of the tension cylinder, which can bemoved relative to one another, are protected by the pressure springsurrounding them.

With respect to the flow of force, the emergency spring cylinder can beconnected parallel or in series to the hydropneumatic spring unit inorder to achieve the effect according to the invention.

In the case of a parallel connection, the emergency spring cylinder canbe arranged to be acting locally next to the hydropneumatic spring unitbetween the superstructure and the bogie. This side-by-side arrangementhas the advantage that, in the case of existing secondary suspensionswith a hydropneumatic spring unit as an active spring element, aretrofitting can take place in a simple manner by adding the emergencyspring cylinder in order to permit an emergency operation in the case ofthe concerned rail vehicles.

As an alternative, it is also conceivable to constructively implementthe solution according to the invention such that the emergency springcylinder coaxially surrounds the hydropneumatic spring unit and isdisengaged in the normal operation, the emergency spring cylinder beingused in the emergency operation. This embodiment of a parallelconnection represents a particularly space-saving solution becauselittle space is required for installing the secondary suspensionaccording to the invention. Another advantage consists of the fact that,also in the emergency operation, parts of the hydropneumatic spring unitcontinue to participate in the power transmission; that is, they do notremain completely unutilized in comparison with the above-explainedembodiment.

A measure further improving the latter embodiment consists of the factthat, for the emergency operation, the hydropneumatic spring unit isvertically guided by means of a coaxial upper pin by way of acorresponding recess on the side of the superstructure. Naturally, it isalso conceivable to arrange the guiding elements in a reverse manner, sothat a pin is arranged on the side of the undercarriage, which pin isvertically guided in a corresponding recess on the side of thehydropneumatic spring unit or the like.

A series connection of the emergency spring cylinder and thehydropneumatic spring unit according to the flow of force is preferablyimplemented in that both constructional units are arranged behind oneanother in the flow of force and therefore act simultaneously. Forreaching the lowered station platform level N_(B) for thesuperstructure, an additional action upon the tension cylinder takesplace in order to compress the pressure spring. In this embodiment, adifference is made in the normal operation between the operation whentraveling and the operation when stopped, that is, at the stationplatform. During travel, the hydropneumatic spring unit acts in serieswith the steel spring of the tension cylinder; that is, the tensioncylinder is pressureless and the steel spring can oscillate. Incontrast, at the station platform, the steel spring is compressed by theaction upon the tension cylinder in order to implement a lowering of therail vehicle to the station platform level N_(B). If the hydropneumaticspring unit fails (system failure), the steel spring takes over thesecondary suspension. The flow of force is created by the direct contactof the piston and the cylinder of the hydropneumatic spring unit in theend stop position, whereby the spring rigidity is also increased in thecase of a corresponding design. It is an advantage of this solution thatthe transverse suspension is maintained as a result of the seriesarrangement. In contrast to the above-described embodiments, here thesteel spring of the emergency suspension is always positioned correctly,so that there are no take-over problems with respect to the latter.

The automatic moving-out of the piston of the emergency spring cylinderpreferably takes place as a result of the pressure drop. As analternative, it is also conceivable that, in the normal operation, thepiston of the emergency spring cylinder remains moved-out while beingdisengaged, the hydropneumatic spring unit ensuring the traveling levelN_(F), and that, after an activating of unlocking devices, the pistoncan at least partially be lowered inside a pot-shaped cylinder housingsurrounding it. This has the effect that also the lowered stationplatform level N_(B) can be reached. In the event of a system failureduring the travel, the normally closed unlocking devices ensure themoved-out position of the piston of the emergency spring cylinder sothat the emergency level N_(N) is ensured by way of the emergency springcylinder. In the event of a system failure in the station, that is,during a stoppage, pressure has to be applied by way of another circuit.This can be achieved by means of a manual operation or by means of thepressure medium stored in an additional storage device.

In the above-described embodiment, the piston of the emergency springcylinder should consist of at least one piston sleeve telescopicallydisplaceable against a spring force into the piston in order to ensurethe spring deflection along the required spring travel. A high springforce can be generated in that an elastomer element is coaxiallysurrounded by a coil spring made of spring steel. By means of thisembodiment, particularly high spring forces can be implemented for asecondary suspension so that a multiple arrangement of emergency springcylinders for the secondary suspension for ensuring the emergencyoperation can possibly be avoided.

It may also be conceivable to completely eliminate the hydropneumaticspring unit in this embodiment. The reason is that the emergency springcylinder of this embodiment can also be used directly for the levelcontrol by way of the admission of pressure medium to the pressurechamber. This will then be a type of vertically adjustable emergencyspring which is locked in the moved-out position of the piston and tothis extent takes over the function of the secondary spring in thenormal operation as well as of the emergency spring in the emergencyoperation.

The system according to the invention for the secondary suspensionhaving a hydropneumatic spring unit as well as an emergency springcylinder which can be acted upon by a pressure medium can be operated bymeans of a single hydraulic circuit or by means of two separatehydraulic circuits. In the case of a single hydraulic circuit, thehydropneumatic spring unit as well as the emergency spring cylinder canbe supplied with pressure medium therefrom. However, the minimal dynamicpressure in a hydraulic accumulator should be sufficiently dimensionedsuch that the pressure spring of the emergency spring cylinder can bekept in the compressed condition. In contrast, in the case of twohydraulic circuits, one hydraulic circuit is assigned to thehydropneumatic spring unit, and the other hydraulic circuit is assignedto the emergency spring cylinder. The advantage of two hydrauliccircuits is in particular that different operating pressures can also beprovided for the two circuits, which results in constructive freedomwith respect to the design and dimensioning of the pressure mediumaggregates.

The hydropneumatic spring unit should preferably comprise a pendulumsupport so that transverse movements between the superstructure and thebogie are permitted and restoring forces are applied for centering thesuperstructure.

In order to implement an active level control between the raisedtraveling level N_(F) and the lowered station platform level N_(B), inaddition, a level sensor is provided for measuring the actual distancebetween the superstructure and the bogie, which level sensor operates asan actual value generator and transmits the electrical measuring signalsto an electronic control unit comprising a regulating unit whichgenerates corresponding adjusting signals for the valve control of thehydraulic circuits based on defined desired values, so that the desiredsuperstructure level can be adjusted by way of the latter. This normallytakes place by way of the hydropneumatic spring unit.

Further measures improving the invention will be indicated in thefollowing together with the description of preferred embodiments of theinvention.

FIG. 1 is a sectional view of a system for the secondary suspension of asuperstructure with an emergency spring cylinder arranged locally nextto an hydropneumatic spring unit, during travel;

FIG. 1 a is a view of the system according to FIG. 1 with the pistonmoved out into the readiness position;

FIG. 2 is a sectional view of the system according to FIG. 1 during theemergency operation;

FIG. 3 is a sectional view of another embodiment of a system for thesecondary suspension of a superstructure with a coaxial arrangement ofthe hydropneumatic spring unit and the emergency spring cylinder, duringtravel;

FIG. 4 is a sectional view of a system according to FIG. 3 during theemergency operation;

FIG. 5 is a sectional view of another embodiment of a system for thesecondary suspension of a superstructure in a series connection of thehydropneumatic spring unit and the emergency spring cylinder, duringtravel;

FIG. 6 is a sectional view of another embodiment of a secondarysuspension for a superstructure with a hydropneumatic spring unit and alockable emergency spring cylinder, during travel;

FIG. 7 is a sectional view of the system according to FIG. 6 during thestop at the station platform; and

FIG. 8 is a sectional view of the system according to FIG. 6 during theemergency operation.

In view of FIG. 1, a hydropneumatic spring unit 3, as the active springelement, is arranged between a top superstructure 1 of a railvehicle—otherwise not shown—and a lower bogie 2. When the rail vehicleis traveling, the hydropneumatic spring unit 3 ensures a raisedtraveling level N_(F) for the superstructure 1, so that the latterremains largely unaffected by disturbing vibrations caused by thetravel. By way of a lower pendulum support 4, the hydropneumatic springunit 3 simultaneously also takes over a transverse guidance of thesuperstructure 1. A pressure chamber 5 of the hydropneumatic spring unit3 is acted upon by way of a hydraulic circuit I. A hydraulic accumulator6 is connected parallel thereto, the integrated gas volume of thehydraulic accumulator 6 ensuring the spring characteristic of thehydropneumatic spring unit 3. As a result of the action upon thepressure chamber 5, the distance between the superstructure 1 and thebogie 2 can be varied. For regulating this superstructure level, a levelsensor 7 is provided for measuring the distance between thesuperstructure 1 and the bogie 2. The level sensor 7 operates as anactual value generator of a level control system integrated in anelectronic control unit—not shown here in detail—, for adjusting thedesired superstructure level.

As a result, the superstructure 1 is raised to an upper traveling levelN_(F) during the normal travel of the rail vehicle. In this position,the maximal spring excursion is ensured for maximum comfort. While therail vehicle stops at the station platform, the superstructure 1 islowered to a lower station platform level N_(B). At this stationplatform level N_(B), the passengers of the rail vehicle can comfortablywalk onto a relatively lower station platform without having to walkover a step.

In addition to the hydropneumatic spring unit 3, an emergency springcylinder 8 is provided locally next to it. The emergency spring cylinder8 becomes active only in the event of a system failure—that is, whenthere is a falling below a minimum pressure in the hydraulic circuitI—and, in this case, ensures an emergency operation for the rail vehicleas a result of the automatic moving-out of a piston 9. During thisemergency operation, the rail vehicle can still be moved at least at alow speed. In the emergency operation, an emergency spring level N_(N)is held by means of the emergency spring cylinder 8, which emergencyspring level N_(N) is situated between the raised traveling level N_(F)and the lowered station platform level N_(B).

In this embodiment, the emergency spring cylinder 8 consists of ahydraulic tension cylinder 9, whose piston 9 can be moved out by meansof a pressure spring 11. Here, the pressure spring 11 is constructed ofsteel in the manner of a coil spring and coaxially surrounds the tensioncylinder 9.

Thus, with respect to the flow of force, the emergency spring cylinder 8is switched parallel to the hydropneumatic spring unit 3 in thisembodiment. In the illustrated position of the piston 9 of the emergencyspring cylinder 8, the secondary suspension is in the normal operationduring travel. This means that the tension cylinder 9 is acted upon bypressure from the hydraulic circuit II, so that the pressure spring 11is compressed and, at this point, the emergency spring cylinder 8 doesnot become operative.

In a modification according to FIG. 1 a, it is provided that, in theevent of a system failure, the emergency spring level N_(N) is adjustedby way of the already moved-out emergency spring cylinder 8.

According to FIG. 2, a system failure results in a pressure drop in thehydraulic circuits I and II so that, on the one hand, the hydropneumaticspring unit 3 can no longer carry out its function of a secondarysuspension; on the other hand, as a result of the pressure drop in thetension cylinder 9, an automatic moving-out of the piston 9 takes placewhich now comes in contact with the super structure 1 and takes over thesecondary suspension in the sense of an emergency operation.

In another embodiment according to FIG. 3, the emergency cylinder 8′surrounds the hydropneumatic spring unit 3′, so that a construction isobtained which is compact as a whole. In the illustrated position in thenormal operation, that is, during travel, the pressure spring 11′ istensioned as a result of the admission of pressure medium by thehydraulic circuit II and is therefore not in contact with thesuperstructure 1. The vertical adjustment of the superstructure leveltakes place by way of the hydraulic circuit I in conjunction with thehydraulic accumulator 6′, as described with respect to theabove-mentioned embodiment.

In the emergency operation, according to FIG. 4, the piston 9′ of thetension cylinder 9 comes to rest on the superstructure 1 because thehydraulic circuits I and II lose pressure. As a result, the pressurespring 11′ relaxes and now takes over the secondary suspension in theemergency operation. For guiding the hydropneumatic spring unit 3′ inthe emergency operation, the latter is equipped with an upper pin 12which is vertically guided inside a corresponding recess on the side ofthe superstructure. Because of the arrangement of the hydropneumaticspring unit 3′ and the emergency spring cylinder 8′, which is concentrichere, the transverse suspension and the supporting by way of thependulum support 4′ are maintained.

The embodiment according to FIG. 5 represents a flow-of-force-relatedseries connection between the emergency spring cylinder 8″ and thehydropneumatic spring unit 3″, which are also arranged concentricallywith respect to one another. In the normal operation as well as in theemergency operation, the hydropneumatic spring unit 3″ and the emergencyspring cylinder 8″ operate simultaneously here in the flow of forcebetween the superstructure 1 and the bogie 2. For reaching the loweredstation platform level N_(B) for the superstructure 1, an action uponthe tension cylinder 9″ by the hydraulic circuit II takes place which isadditional with respect to the normal operation, in order to compressthe pressure spring 11″. The hydropneumatic spring unit 3″ fails in theemergency operation, so that the now moved-out pressure spring 11″ takesover the secondary suspension. Also here, the transverse suspension ismaintained as a result of the pendulum support 4″ integrated in the flowof force. In the normal operation, the raised traveling level N_(F) aswell as the lowered station platform level N_(B) are regulated by way ofthe hydraulic circuit I—as described above.

In another embodiment according to FIG. 6, it is illustrated that, inthe shown normal operation, an emergency spring cylinder 8′″ arrangednext to the hydropneumatic spring unit 3′″ is disengaged. However, thepiston of this emergency spring cylinder 8′″ has fully moved out. Thehydropneumatic spring unit 3′″ ensures the raid traveling level N_(F) aswell as the lowered station platform level N_(B).

For taking up the lowered station platform level N_(B), the piston 9′″can be lowered inside a pot-shaped cylinder housing 14, as illustratedin FIG. 7, after the activating of unlocking devices 13 which areconstructed here in the manner of a lockball mechanism.

In the event of a system failure, thus, in the emergency operation, thenormally closed unlocking devices 13, which can be unlocked by way ofthe hydraulic circuit II, ensure the moved-out position of the piston9″, as illustrated in FIG. 8. The secondary suspension is now ensured byway of a spring arrangement integrated in the piston 9′″, which springarrangement is formed of an elastomer element 15 as well as of apressure spring 17 in the manner of a coil spring surrounding theelastomer element 15. The spring effect is achieved by way of a pistonsleeve 16 which can be moved in and out relative to the piston 9′″corresponding to the spring travel and comes to rest on the lower bogie2. The piston 9′″ can be changed into the moved-out position by way of apressure spring 19 interacting with the pot-shaped cylinder housing 14,by way of the weight as well as additionally by way of admittingpressure medium to the pressure chamber constructed in the cylinderhousing 14, in which moved-out position, the emergency spring cylinder8′″ is locked in its moved-out position.

The embodiment according to FIG. 9 represents the coaxially integratedvariant of the embodiment according to FIG. 1. The system is shown inthe normal operation at the stop (station platform). For lowering thesuperstructure 1 to the station platform level, circuit II is acted uponby compressed air, so that the pressure spring 11′″ is compressed whichacts as an emergency spring. Simultaneously, oil in the hydropneumaticcircuit I is discharged in order to lower the superstructure 1. Afterthe loading of the superstructure at the station stop has beenconcluded, oil is admitted to circuit I and the pressure in circuit IIis lowered, so that the superstructure 1 rises to the traveling level.The fixed stop 20 formed by a step in the interior is now ready to takeover the emergency spring function. Specifically, if the hydropneumaticcircuit I fails, the superstructure 1 is lowered onto the stop 20, sothat the pressure spring 11′″ takes over the emergency suspension.

In the normal operation during travel, the circuit II is pressureless.The secondary suspension takes place by way of the hydropneumaticcircuit I. Depending on the adjustment of the pressures, it can beachieved that the pressure spring 11′″ stands still or participates inthe suspension in the normal operation.

With respect to its implementation, the present invention is not limitedto the above-described four concrete embodiments. On the contrary,modifications thereof are also conceivable which use the teaching of theclaims which follow. Thus, it is also conceivable to use also a singlehydraulic circuit besides a preferred separate admission of pressuremedium to the hydropneumatic spring unit and the emergency springcylinder by way of separate hydraulic circuits. However, in that case,the valve wiring would have to be correspondingly adapted. For ensuringa transition from the normal operation to the emergency operation thatis as smooth as possible, the solution according to the inventionprovides that the pressure control of the hydraulic circuit II isanalyzed by the level detection of the sensor or the analysis ofpressure gradient courses and is controlled correspondingly with respectto time.

List of Reference Numbers

-   1 superstructure-   2 bogie-   3 hydropneumatic spring unit-   4 pendulum support-   5 pressure chamber-   6 hydraulic accumulator-   7 level sensor-   8 emergency spring cylinder-   9 tension cylinder-   10 piston-   11 pressure spring-   12 pin-   13 unlocking device-   14 cylinder housing-   15 elastomer element-   16 piston sleeve-   17 pressure spring-   18 pressure chamber-   19 pressure spring-   20 stop

1. System for the secondary suspension of a superstructure (1) in thecase of a rail vehicle, having a hydropneumatic spring unit (3) as anactive spring element which is placed between the superstructure (1) anda bogie (2) arranged below it and which ensures at least one raisedtraveling level (N_(F)) for the superstructure when the rail vehicle istraveling, characterized in that, by way of the hydropneumatic springunit (3) as the active spring element, in the normal operation, inaddition to the raised traveling level (N_(F)), a lowered stationplatform level (N_(B)) can be adjusted for the superstructure (1),additionally at least one emergency spring cylinder (8) being providedwhich, when the system fails, ensures an emergency spring level (N_(N))situated in-between for an emergency operation.
 2. System according toclaim 1, characterized in that the emergency spring level (N_(N)) isadjusted in the event of a system failure by means of an automaticmoving-out of the emergency spring cylinder (8) (FIG. 1).
 3. Systemaccording to claim 1, characterized in that the emergency spring level(N_(N)) is adjusted in the event of a system failure by way of thealready moved-out emergency spring cylinder (8) (FIG. 1 a).
 4. Systemaccording to claim 1, characterized in that the emergency springcylinder (8) comprises a hydraulic piston (10) which is surrounded by atension cylinder (9) and can be moved out by means of a pressure spring(1).
 5. System according to claim 4, characterized in that the pressurespring (11) is constructed of steel in the manner of a coil spring whichcoaxially surrounds the tension cylinder (9).
 6. System according toclaim 1, characterized in that, with respect to the flow of force, theemergency spring cylinder (8) is connected parallel to thehydropneumatic spring unit (3).
 7. System according to claim 6,characterized in that the emergency spring cylinder (8) is arranged tobe acting locally next to the hydropneumatic spring unit (3) between thesuperstructure (1) and the bogie (2) (FIGS. 1 to 2).
 8. System accordingto claim 6, characterized in that the emergency spring cylinder (8′)coaxially surrounds the hydropneumatic spring unit (3′) and isdisengaged during the normal operation, the emergency spring cylinder(8′) being used in the emergency operation (FIGS. 3 and 4).
 9. Systemaccording to claim 8, characterized in that, for the emergencyoperation, the hydropneumatic spring unit (3′) is vertically guided bymeans of a coaxial upper pin (12) by way of a corresponding recess onthe side of the superstructure (1) in order to ensure the emergencysuspension by means of the emergency spring cylinder (8′).
 10. Systemaccording to claim 1, characterized in that, with respect to the flow offorce, the emergency spring cylinder (8″) is connected in series withrespect to the hydropneumatic spring unit (3″), so that the twoconstruction units act simultaneously, for the reaching of the loweredstation platform level (N_(B)) for the superstructure (1), an additionalaction upon the tension cylinder (9″) taking place in order to compressthe pressure spring (11″).
 11. System according to claim 1,characterized in that the automatic moving-out of the tension cylinder(9) takes place as a result of the pressure drop in the emergency springcylinder (8).
 12. System according to claim 7, characterized in that, inthe normal operation, the piston (10′″) of the emergency spring cylinder(8′″) has moved out in a disengaged manner, the hydropneumatic springunit (3″) ensuring the traveling level (N_(F)), and in that, after theactivating of unlocking devices (13), the piston (10′″) can be at leastpartially lowered inside a pot-shaped cylinder housing (14) surroundingit, in order to reach the lowered station platform level (N_(B)), in theevent of a system failure, the normally closed unlocking devices (13)ensuring the moved-out position of the piston (10′″), so that theemergency level (N_(N)) can be ensured by way of the emergency springcylinder (8′″) (FIGS. 6 to 8).
 13. System according to claim 12,characterized in that the piston (10′″) comprises at least one pistonsleeve (16) which can be telescopically displaced against a springforce.
 14. System according to claim 12, characterized in that thespring force can be generated by a coaxial arrangement of an elastomerelement (15) surrounded by a pressure spring (17′″).
 15. Systemaccording to claim 7, characterized in that the piston (10′″) can bechanged into the moved-out position by way of a pressure spring (19)interacting with a pot-shaped cylinder housing (14), by way of theweight and, in addition, by way of an admission of pressure medium to apressure chamber (18) of the cylinder housing (14).
 16. System accordingto claim 4, characterized in that two hydraulic circuits (I, II) areprovided, one hydraulic circuit (I) supplying the hydropneumatic springunit (3) and the other hydraulic circuit (II) supplying the emergencyspring cylinder (8) with pressure medium.
 17. System according to one ofthe preceding claims, characterized in that the hydropneumatic springunit (3) comprises a pendulum support (4) for transmitting transversemovements between the superstructure (1) and the bogie (2).
 18. Systemaccording to one of the preceding claims, characterized in that a levelsensor (7) is provided for measuring the distance between thesuperstructure (1) and the bogie (2), which level sensor (7), as anactual value generator, is a component of an active level control foradjusting a desired superstructure level.
 19. System according to one ofthe preceding claims, characterized in that the level sensor (7) formeasuring the distance between the superstructure (1) and the bogie (2)is simultaneously used for activating the emergency spring cylinder. 20.System according to one of preceding claims, characterized in that, forthe implementation of the at least one hydraulic circuit (I, II), ahydraulic unit is used which comprises at least one hydraulicaccumulator (6) for the hydropneumatic suspension.
 21. System accordingto one of the preceding claims, characterized in that a pressure sensoris provided in the hydraulic circuit (I), the electronic analyzingsystem connected on the output side of the pressure sensor activatingthe emergency spring cylinder (8) when the pressure drops below a lowerlimit value.